Small objects such as pills or capsules are typically marketed in blister packs comprising a base film formed with an array of blisters or pockets each holding one or more of the objects and a cover film sealed to a face of the blister film in the webs between the pockets. Such a package is made normally in a continuous manner by advancing the blister film with its pockets open upward first through a filling station where the objects are loaded into the pockets and then through a sealing station where the cover film is applied to the upper face of the blister film and sealed to it, typically by heat.
In the sealing station the blister film is advanced in a travel direction by a constantly rotating drive roll having a cylindrical surface formed with an array of recesses into which the pockets fit, so the drive roll pulls the blister film through the sealing station. A heated sealing roll with a smooth cylindrical surface and centered on an axis presses the cover film downward against the drive roll and seals the two films together. The two films leave the sealing station laminated together and hermetically containing the objects. Such machines are described in German patent documents 197 40 191, 100 52 218, and 10 2004 062 520.
A problem with such systems is that the products to be sealed, such as, for example, tablets, capsules, coated pills, or the like that are to be filled into the blisters and that are to be enclosed by the cover and blister film, are not in the blisters but instead are located adjacent thereto on the cover film on the webs between the blisters. This can be caused, first of all, by misfeeds that leave the products to be sealed resting next to the blisters. Second, during transport of the cover film the products can move out of the blisters due to vibration or movements of the cover film. The objects can also move out of the blisters due to static loads or human intervention.
Typically, these incorrectly placed products can be detected by angled brushes or by safety flaps and removed. Nevertheless, a situation can occur in which products are still on the webs between the blisters even after passing these quality-control devices. In this case the two films enter the gap between the sealing roll and feed roll not in surface contact at the webs, but held at a spacing by an object that is out of place. As the thus spread films pass through the sealer, the tablet is partially crushed, thereby contaminating the package being produced. If not culled out, such a package can get to the consumer spoiled and, in the case of a medicament, create a potentially dangerous situation.
Furthermore an object not in a blister and wedged between the films pushes the sealing roll away from the feed roll, so that an entire row of packages is not sealed and must be rejected. This requires a meticulous downstream inspection to locate and cull such defective packages.